With applications ranging from diagnostic procedures to radiation therapy, the importance of high-performance medical imaging is immeasurable. As such, new advanced medical imaging technologies continue to be developed. Some such imaging systems utilize amorphous silicon flat panel x-ray detectors.
Generally, in amorphous silicon flat panel x-ray detectors, an amorphous silicon array is disposed on a glass substrate, and a scintillator is disposed over, and is optically coupled to, the amorphous silicon array. The amorphous silicon array comprises pixels, typically arranged in a matrix of rows and columns. During operation, an x-ray source emits a beam of x-rays towards the scintillator, which absorbs the x-ray photons and converts them to visible light. The amorphous silicon array then detects the visible light and converts it into electrical charge. The electrical charge at each pixel on the amorphous silicon array is then read out digitally by low-noise electronics, and is sent to an image processor. Thereafter, the image is displayed on a display, and may also be stored in memory for later retrieval.
Optimal images, both in terms of resolution and contrast, are achieved when the scintillator absorbs the incident x-ray photons and emits visible light in response thereto that is detected substantially only by the photodiodes that are directly underlying the regions of the scintillator where the x-ray photons were first absorbed. However, in practice, the visible light is generated not only over the photodiodes, but also over other areas of the panel. Additionally, the visible light may be scattered so that not all light generated at one position strikes the amorphous silicon array directly underlying that position. Furthermore, due to its photoconductive nature, a FET that is exposed to light may become conductive and allow charge to leak through it when the gate voltage is held low. This leaking charge may then be read out as an added signal in pixels on the same data line that are read out before the leaking FET. To prevent this from happening, a light-blocking layer is often utilized over the FETs to prevent the FETs from being exposed to light.
While light-blocking layers have many benefits, there are also drawbacks to using them as they currently exist. Existing light-blocking layers, such as those described in U.S. Pat. No. 6,396,046 (issued to Possin et al.), cover all the FETs in the amorphous silicon array to prevent the FETs from being exposed to light. This is more cover than is needed to get rid of artifacts caused by FET photoconductivity. Additionally, in some detectors, the light-blocking layer comprises a layer close to the data line, which increases the capacitive coupling between the data line and the light-blocking layer. This causes an increase in electronic noise.
Since light can cause FET photoconductivity, which can significantly degrade the performance of an amorphous silicon flat panel x-ray detector, improved light-blocking layers are needed. Therefore, it would be desirable to have light-blocking layers that prevent or minimize artifacts caused by FET photoconduction, while causing a minimal increase, if any, in data line capacitance and electronic noise. It would also be desirable to have light-blocking layers that are patterned so as to block light from only a portion of the total number of FETs in the device. It would be even further desirable to have light-blocking layers that are patterned so as to block light from only those FETs in the device that are read out last, since they are the major contributors to the FET photoconductive leakage problem.